Lead wires for firing devices



news, 1940. I c. HUNT 2,218,170

LEAD WIRES FOR FIRING DEVICES Filed Dec. 16, 1938 FIG. I

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IIIIIIII'IIIIIII VIII II/IIIIIIIIIIII IIIIII IIIIIIIxII/IIA IIIIIIII IIIIIIIIIIII/f' 'IIIIIIIII WILLIAM c. HuN'r INVENTOR ATTORNEY Patented Oct. 15, 1940 PATENT OFFICE LEAD WIRES FOR FIRING DEVICES William 0. Hunt, Wilmington, Del.,, assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Application December 16, 1938, Serial No. 246,060

9 Claims.

This invention relates to an improvement in blasting caps and more particularly to the provision of means whereby accidental firing of a cap through contactof the lead wires with a source of'current will be positively avoided.

As is well known, electric blasting caps comprise a container which holds a detonating charge, for example diazo-dinitrophenol. Within said container a firing assembly is provided lo which includes a bridge wire embedded within the detonating charge itself or within a more readily fired ignition charge. From the said bridge wire extend two insulated lead wires of such a convenient length that they may be attached to a source of electric current for the purpose of firing the said blasting cap. To facilitate the connection of these insulated lead wires to the source of current it has been the accepted practice of the prior art to furnish about two to about three inches of bare wire at the ends of the said insulated lead wires. To provide about two to three inches lof bare wire at the ends of the insulated lead Wires, it is necessary to remove the insulation in some manner.

It has been well recognized that the uninsulated portion of the lead Wires constitute a hazard in that they afford an opportunity for the accidental discharge of the cap. This accidental an discharge is easily possible since, for example, .in a mine the lead wires are frequently trailed and are\likely to come into contact with a live circuit or a stray current as, for example, a trolley line or a charged rail. To prevent the 5 possibility of premature explosions various means of shunting the lead wires have been suggested, but have been for many reasons found unsatisfactory. I

The many shunting methods now in use, such 4 as twisting the wires together or bridging the wires with various types of metal shunts, have been found unsatisfactory since the shunted wires are hard to separate without considerable distortion. This distortion of the bare ends of 5 the lead wires makes their use dii'licult, as tightelectrical connections are harder to obtain The bare ends of the lead wires often become co-rroded and thus when caps are put into use it may be necessary to clean these ends to insure 50 efiicien-t connection to the firing circuit.

It is the object of this invention to provide means whereby the difliculties of protecting the lead wires are overcome.

, Now inaccordance with this invention, I have 5 found that the insulation covering the lead wires of electric blasting caps may be weakened by cutting, nicking, crushing, or deforming the insulation at the required distance from the ends of the wire so that a suflicient portion of the insulation, for example about two to three inches, 5 may be removed from the ends of the wires to allow electrical connection. When the firing device is to be connected to the firing circuit, the operator will easily strip oif about twoto three inches of insulation, -due to the cut or 10 nicked condition of the insulation, and so provide himself with the undeformed and uncorroded bare ends that will make easy and positive electrical contact with the firing circuit.

Thus, by allowing the original insulation to re- 15 I extruded plastic compositions which loosely adhere to the wire. I have found that plastic materials, for example, of the polymerized vinyl ester type, phenol aldehyde type, urea aldehyde type, cellulose acetate type and cellulose mixed esters type, may be suitably modified for use as insulating compounds in accordance with my invention.

The more generally used types of insulating materials, for example cotton-thread and paper, have also been found suitable when they are impregnated with a saturant, such as paraflin, to a degree that causes the insulation to adhere loosely to the wire.

Now I have found that it may be desirable with my invention to include the addition of a means to further protect the nicked lead wires by adding to the individual wires a globule of 5 material that will cover the bare metal exposed at the termination of the wire. The addition of this globule, while not essential, gives the metal exposed at the wire ends an added degree of protection. This globule on the end of the wire may consist of a resin or a, plastic, for example, rosin, ester gum, phenoialdehyde products, damar, cellulose acetate or other suitable materials that will adhere to the wire ends. A

further modification of this invention may also v include the protection of any bare wire that is exposed in the nicking, cutting, or crushing process by covering these exposed areas with the same or similar resins or plastics which are found suitable for protecting the wir ends.

These aforementioned insulating materials may be removed easily by the stripping action of the thumb and forefinger when, in accordance with this invention, they have been carefully prepared by cutting, nicking, or crushing at the proper point. Thus the firing device with lead wires processed in accordance with this invention is protected from accidental discharge until ready to be connected into the firing circuit.

Having now indicated in a general way the nature and purpose of this invention there follows a description of a preferred embodiment thereof as shown by the accompanying drawing in which:

Figure 1 shows a firing device with lead Wires prepared in accordance with this invention.

Figures 2, 3, and 4 indicate the varying means and forms of weakening the insulation of the lead wires in order to effect easy removal.

Referring to Figure 1, the firing device I from which extends a pair of completely insulated lead wires 2 may be of any type used for the firing of any commercial explosive. The lead wires 2 are of any convenient length and may be further packaged in any of the various forms well known to the art. At a sufficient distance from the loose ends of the completely insulated lead wires 2 the insulation surrounding the wire proper is weakened 3, this weakening process providing for the easy removal of insulation from the portion 4, thereby furnishing upon removal of the insulation from portion 4 sufllcient bare wire to allow connection to an electrical circuit.

In Figure 2 the enlarged lead wires 2 show the insulation 5 after cutting with a knife at 3, thereby furnishing completely severed insulation which may be easily stripped from the wire 6.

Figure 3 is similar to Figure 2 except that the insulation 5 has been crushed at the point 3 as by plier jaws or other suitable means, thereby allowing easy stripping of the insulation from the wire 6.

Figure 4 is similar to Figure 2 except that the insulation 5 has been nicked at 3 instead of completely severed. This nicking at 3 is sufficient to weaken the insulation 5 to allow easy removal from the wire 6.

There are various methods of crushing, cut-' ting, or severing the wire insulation which will suggest themselves to those skilled in the art. A specific example of a suitable method of crushing the insulation to allow the easy removal oi! the said. insulation from the wire would be a mounted crushing tool similar to a pair of pliers, the jaws of which may be grooved in such a manner as to provide protection to the wire proper while the insulation is being completely crushed at any designated point. The provision for stops and guides to aid the proper manipulation of the said wire and jaws will be obvious. This crushing tool may be of other various designs such as rolls thru which the wire must pass, or an arranged chuck head which will clamp the insulation tightly, or any other suitable design for crushing the said insulation to provide for easy removal of the end portions from the wire.

As another specific example of a method of rendering the insulation of the wires suitable for easy removal of the end portions of insulation there may be employed a device having knives to cut cleanly the insulation at the desired point. The cutting of the insulationmay be accomplished by either revolving the wire against a knife, or by passing the wire between knives so set as to cut thru the insulation. It is also contemplated to use stops and guides to facilitate the proper cutting of the insulation and likewise to prevent the deforming or damaging of the wire itself.

Blasting caps with lead wires prepared in accordance with this invention are advantageous over caps of the prior art in that there is absolute protection from stray currents or live circuits, and the wire ends are not distorted or deformed,

which allows surer and easier electrical connection.

It will be understood that the details and examples given hereinbefore are-illustrative only, and in no way limiting on my invention as broadly described hereinbefore and in the appended claims.

What I claim and desire to protect by Letters Patent is:

1. A firing device lead wire provided with complete protection against accidental contact with a source of E. M. F., but easily connectable thereto, in electrically conducting relation, which comprises a metallic wire completely insulated with an adhering but removable insulation, said insulation weakened at a predetermined point from the end to provide removal by stripping of a portion of the said insulation whereby a section of bare wire sumcient to allow electrical connection to a source of E. M. F. is exposed.

2. An electric blasting cap lead wire provided with complete protection against accidental contact with a source of E. M. F., but easily connectable thereto, in electrically conducting relation, which comprises a metallic wire completely insulated with an adhering but removable insulation, said insulation weakened at a predetermined point from the end to provide a removable portion which when stripped from the wire exposes a section of bare metallic wire sufiicient to allow electrical connection to a source of E. M. F.

3. Lead wires for electric firing devices, having complete protection against accidental contact with a source of E. M. F. but easily connectable thereto, in electrically conducting relation, which comprises a pair of metallic wires completely insulated with an adhering but removable insulation, said insulation weakened at a predetermined point from the end of each of the pair of wires to provide removal by stripping a portion of the said insulation whereby a section of bare metallic wire suflicient to allow electrical connection to a source of E. M. F. is exposed at the ends of each of the pair of the said lead wires. V

4. An electric blasing cap lead wire provided with complete protection against accidental contact with a source of E. M. F., but easily connectable thereto, .in electrically conducting relation, which comprises a metallic wire completely insulated with an adhering but removable, impregnated type insulation, said insulation weakened at a predetermined point from the end to provide a removable portion which when stripped from the wire exposes a section of bare metallic wire suflicient to allow electrical connection to a source of E. M. F.

5. An electric blasting cap lead wire provided with complete protection against accidental contact with asource of E. M. F., but easily connectable thereto, in electrically conducting relatlon, which comprises a metallic wire completely insulated with an adhering but removable phenolaldehyde type plastic insulation, said insulation with complete protection against accidental contact witha source. of E. M. F., but easily con-- nectable thereto, in electrically conducting relation, which comprises a metallic wire completely insulated with an adhering but removable, poly- Inerized vinyl ester type plastic insulation, said insulation weakened at a predetermined pointfrom the end to provide a removable portion which when stripped from the wire exposes a section of bare metallic wire suflicient to allow electrical connection to a source of F.

7. An electric blasting cap lead wire provided with complete protection against accidental contact with a sourceof E. M. F., but easily connectable thereto, in electrically conducting relation, which comprises a metallic wire completely insulated with an adhering but removable impregnated cotton thread type insulation, said insulation weakened at a predetermined point from the. end to provide a removable portion which when stripped from the wire exposes a section of bare metallic wire sufficient to allow electrical connection to a source of E. M. F.

8. In the preparation of lead wires for electric blasting caps having complete protection against accidental contact with a source of E. M. R, but easily connectable thereto, in electrically conducting relation, and which comprises a pair of metallic wires completely insulated with an adher-.

ing but removable insulation which is weakened at a predetermined pointfrom the end to provide removal by stripping of a portion of said insulation in order to expose bare metallic wire to allow electrical connection to a source of E. M. F., the step of protecting exposed bare wire at the point where the said insulation was weakened and at the ends of the said lead wires by the application of a globule of insulating material to the said exposed bare wire surfaces.

9. In the preparation of lead wires for electric blasting caps having complete protection against accidental contact with a source of E. M. F., but easily connectable thereto, in electrically conducting relation, and which comprise a pair of metallic wires completely insulated with an adhering but removable insulation which is weakened at a predetermined point from the end to provide-removal by stripping of a portion of said insulation in order to expose bare metallic wire to allow electrical connection to a source of E. M. F., the step of protecting exposed bare wire by the application of a globule' of insulating material to the said exposed bare wire surfaces.

WILLIAM C. HUNT. 

